TWI716986B - Nitride semiconductor device and substrate thereof, method for forming rare earth element-added nitride layer, and red light emitting device - Google Patents

Abstract

An objective of the present invention is to provide a technique for manufacturing nitride semiconductor layer, which eliminates the risk of lattice distortion and crystal defects due to crystal-mixing with GaN when a semiconductor device is manufactured by forming a nitride semiconductor layer on an off-angle tilted substrate,, and by which it is possible to stably supply high-quality semiconductor devices by using materials that do not require continuous addition and therefore preventing occurrence of macrosteps.

As a solution, the present invention provides a nitride semiconductor device, which is constituted by providing a nitride semiconductor layer on a substrate, wherein the substrate is an off-angle tilted substrate, a rare earth element-added nitride layer to which a rare earth element is added is provided on the substrate as a base treatment layer, and a nitride semiconductor layer is provided on the rare earth element-added nitride layer.

Description

Nitride semiconductor device, its substrate and method for forming nitride layer added with rare earth elements, and red light emitting device

The present invention relates to a method for forming a nitride semiconductor device, its substrate and a nitride layer added with rare earth elements, and a red light-emitting device and its manufacturing method.

In recent years, light-emitting devices such as light-emitting diodes (LED: Light Emitting Diode) and laser diodes (LD: Laser Diode) have been widely used. For example, the LED system is used in various display devices, mobile phones and other liquid crystal display backlights, white lighting, etc. On the other hand, the LD system is used as a light source for Blu-ray discs for high-vision video recording and reproduction. , Optical communications, CD, DVD, etc.

In addition, recently, high-frequency devices such as MMIC (monolithic microwave integrated circuit) and HEMT (High Electron Mobility Transistor) for mobile phones are used in reverse for automotive-related applications.器(inverter, also known as reverse The applications of high-output power devices such as power transistors and Schottky-Barrier Diodes (SBD) are expanding.

Semiconductor elements constituting these devices are usually manufactured by forming nitride semiconductor layers such as gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), etc. on a substrate such as sapphire.

Conventionally, as a method of forming a nitride semiconductor layer on a substrate, a method of growing crystals on the (0001) (c-plane) of the nitride semiconductor layer substrate is generally used. However, in this method, it is caused by the film formation. Deformation causes piezoelectric (piezo) polarization and sometimes causes the problem that the device characteristics as originally expected cannot be obtained. That is, the internal electric field is generated in the nitride semiconductor layer along with the generation of the piezoelectric polarization and the wave function of electrons and holes are separated, so that the probability of radiation recombination in the nitride semiconductor layer is low and the expected device characteristics cannot be displayed. The situation.

Therefore, it has been studied to use a substrate with a slightly inclined surface to the c-plane (off angle inclined substrate) and use the slightly inclined surface as the film forming surface to make it slightly inclined from the [0001] direction along the crystal axis The azimuthal growth of several degrees exerts multiple advantages such as reduction in the density of crystal defects of the nitride semiconductor layer and improvement in luminous efficiency, and also seeks to improve device characteristics (for example, Patent Document 1).

Fig. 8 is a diagram illustrating the crystal growth using the obliquely inclined substrate. Ga is represented by the large circle on the right side of the lower part of Fig. 8 and is adsorbed along the center of the adjacent c-plane by a separation distance c. GaN crystal grows. Furthermore, as shown in the center of the lower part of Fig. 8, the c-plane is inclined by an angle θ. This result, as shown in the upper part of Figure 8, the height of the step (the thickness of the Ga-N monolayer) in the obliquely inclined substrate is (c/2), and the width of the terrace (the width at which Ga atoms can diffuse) ) Is (c/2tanθ).

However, in the case of this method, there is obviously a new problem, that is, when the oblique angle is excessively increased in order to reduce the crystal defect density and drastically improve the luminous efficiency, etc., because the width of the platform suddenly becomes narrow, Thus, with the step bunching mechanism, a huge giant Macrostep, and the device characteristics as designed cannot be obtained when manufacturing nitride semiconductor light-emitting devices and electronic devices.

Figure 9 is a diagram specifically showing the relationship between the bevel angle and the platform width. The vertical axis is the platform width and the horizontal axis is the bevel angle θ. It can be seen from Figure 9 that the width of the platform and the size of the bevel angle are inversely related. Only by changing the bevel angle θ from 0.15° to 1°, the width of the platform suddenly narrows from 99.0nm to 14.9nm. Moreover, when the width of the platform is too narrow, step folds are generated and giant steps with a large step height appear.

When such a giant step appears, according to the difference in the introduction efficiency of the atomic species (such as Ga) near the step, a strong composition distribution is generated in the crystal during the production of mixed crystal (such as AlGaN), and is affected by the quantum well structure. The manufacturing of nanostructures that require control at the order of several nanometers has a significant impact on device characteristics. Particularly in the field of light-emitting devices, there are many issues such as difficulty in tight control of the emission wavelength in practical applications.

Furthermore, even after the surface of the substrate is smoothed by polishing and etching, the giant step reappears when the nitride semiconductor layer is formed thereon, so the device characteristics as designed still cannot be obtained.

Therefore, in order to manufacture high-quality and high-performance nitride semiconductor light-emitting devices and electronic devices as designed, it is considered that a crystal growth technology that maintains a flat surface without giant steps is indispensable. For example, it has been proposed to add indium (In) to the nitride. Technology (Non-Patent Document 1).

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2004-335635 A

[Non-Patent Literature]

[Non-Patent Document 1] CKShu and 4 others "Isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition (Isoelectronic In-doping effect on the growth of GaN films by metalorganic chemical vapor deposition)" , Appl. Phys. Lett. (Applied Physics Communications) 73, 641 (1998)

However, it is known that there are various problems in the addition of In. For example, the addition of In may be mixed with GaN to form InGaN. Since the formation of InGaN may cause lattice deformation and crystal defects, strict flow control is necessary. In addition, In must continue to be added when the giant ladder is removed.

Therefore, the subject of the present invention is to provide a manufacturing technology of a nitride semiconductor layer, which does not cause lattice distortion as In and GaN mixed crystals when forming a nitride semiconductor layer on an obliquely inclined substrate to manufacture a semiconductor device In addition, the use of materials that do not need to be added prevents the generation of macrosteps, so that high-quality semiconductor devices can be supplied stably.

The inventor of the present invention succeeded in manufacturing a red light-emitting diode with a GaN layer (Eu-added GaN layer) added with Eu (Europium), which is one of the rare earth elements, as a light emitting layer in the world. Organometallic vapor phase epitaxial growth of Eu-added GaN layer (epitaxial) (OMVPE method) The department has reached a level that others cannot imitate.

In the process of the present inventors, they learned that the surface of the Eu-added GaN layer is flattened and found that Eu has a surfactant effect. Therefore, when a nitride semiconductor thin film is formed on an obliquely inclined substrate to manufacture a semiconductor device, when a Eu-added GaN layer is provided on the obliquely inclined substrate as a base treatment layer, the surfactant effect of Eu can be exerted And considering whether the growth of the nitride semiconductor layer can prevent the generation of giant steps, various experiments and studies have been conducted.

As a result, it was found that even if Eu was added at a low concentration of 1at% or less, the giant step system on the obliquely inclined substrate surface was significantly reduced when the Eu-added GaN layer was grown, and even when Eu was added to the GaN layer A GaN layer with a thickness greater than 5μm without Eu addition does not produce giant steps and can form a flat surface at the atomic level. By adding Eu, the effect of maintaining the flat surface can be obtained, which is also very interesting academically. the result of.

At present, we are still trying to understand the mechanism behind this phenomenon that the addition of Eu can prevent the generation of giant steps. However, it has been speculated that the addition of In promotes the diffusion of Ga atoms for smoothing. In contrast, Eu is By hindering the diffusion of Ga and preventing the generation of giant steps, it exerts an excellent surfactant effect and smoothes the surface of the Eu-added GaN layer and the Eu-free GaN layer formed thereon.

Moreover, the addition of Eu at a lower concentration of 1 at% or less is different from the addition of In, and there is no need to continue to add. In addition, the lower concentration of Eu will not be mixed with In and GaN to form InGaN. Because it is added in a way that partially replaces GaN's Ga, it does not cause crystal defects and requires no strict flow rate. control.

In this way, strict flow control and continuous addition are not required, and its significance can be said to be very significant in the actual manufacturing of nitride semiconductor devices.

Moreover, in the present invention, by providing the Eu-added GaN layer as the base treatment layer, the generation of giant steps can be prevented, so not only light-emitting devices, but also high-frequency devices and high-output devices can be stably supplied with suitable nitrogen.化物 Semiconductor device.

Furthermore, in further experiments and discussions regarding the preferred concentration of Eu and the thickness of the GaN layer with Eu added, it is found that the preferred concentration of Eu in the Eu added GaN layer is 0.001 to 10 at%. The thickness of the Eu-added GaN layer is preferably 0.1 nm or more. The upper limit of the thickness of the Eu-added GaN layer is not particularly specified. However, considering the saturation of surface smoothing accompanied by the surfactant effect of Eu, it is considered that a sufficient effect can be obtained with a thickness of about 2 μm.

In addition, in the above description, GaN is used as a nitride and Eu is used as an additional element. However, when the inventor further conducted experiments and studies, it was found that even so-called GaN-based nitrides (including InGaN) such as AlN and InN other than GaN , AlGaN, etc.) as a nitride, it also has approximately the same chemical properties as GaN and can be handled in the same way. It is also known that the additive element is not limited to Eu. As long as it has the same chemical properties as Sc, Y, and La up to Lu, the rare earth elements collectively called Lanthanoids will be in comparison with Eu. The same excellent surfactant effect can be exerted under the same conditions.

Furthermore, when conducting research on substrates, it was found that in addition to sapphire, SiC and Si can also be used as substrates. The same surfactant effect can be obtained by providing a nitride layer added with a rare earth element such as an Eu nitride layer. . The SiC system is suitable for manufacturing high-power devices because of its high thermal conductivity and excellent heat dissipation. Moreover, since Si is inexpensive and can be easily obtained in a large size, it is suitable for manufacturing nitride semiconductor devices at low prices. It is also preferable to use a nitride semiconductor composed of GaN, InN, AlN, or a mixed crystal of any two or more of these.

The inventions described in items 1 to 7 of the scope of patent application are inventions based on the above-mentioned insights. The invention described in item 1 of the scope of patent application,

A nitride semiconductor device is constructed by placing a nitride semiconductor layer on a substrate, and is characterized in that:

The aforementioned substrate is an obliquely inclined substrate,

A nitride layer added with rare earth elements is provided on the aforementioned substrate as a base treatment layer, and the aforementioned nitride layer added with rare earth elements is one added with rare earth elements,

A nitride semiconductor layer is provided on the aforementioned nitride layer added with rare earth elements.

Moreover, the invention described in item 2 of the scope of patent application,

The nitride semiconductor device described in claim 1, wherein the nitride layer with the rare earth element added is a mixed crystal in which the rare earth element is added to GaN, InN, AlN, or any two or more of these Into the layer.

Also, the invention mentioned in item 3 of the scope of patent application,

The nitride semiconductor device described in item 1 or 2 of the scope of the patent application, wherein the addition concentration of the rare earth element in the nitride layer to which the rare earth element is added is 0.001 to 10 at%.

Moreover, the invention described in item 4 of the scope of patent application,

The nitride semiconductor device described in any one of items 1 to 3 in the scope of the patent application, wherein the thickness of the nitride layer to which the rare earth element is added is 0.1 nm or more.

In addition, the inventions mentioned in the 5 items of the scope of patent application,

The nitride semiconductor device described in any one of items 1 to 4 in the scope of patent application, wherein the rare earth element is Eu.

Moreover, the invention described in item 6 of the scope of patent application,

The nitride semiconductor device described in any one of items 1 to 5 in the scope of the patent application, wherein the aforementioned The substrate is any one of sapphire, SiC, and Si, or a nitride semiconductor composed of GaN, InN, AlN, or a mixed crystal of any two or more of these.

In addition, the invention described in item 7 of the scope of patent application,

The nitride semiconductor device described in any one of items 1 to 6 of the scope of patent application is any one of a light emitting device, a high frequency device, and a high output power device.

In the above, the nitride semiconductor device is manufactured by providing a nitride semiconductor layer without rare earth elements after providing a rare earth element-added nitride layer on an oblique angle substrate as a base treatment layer. However, it is prepared in advance by forming a nitride layer with rare-earth elements added on an obliquely inclined substrate as a substrate and provided to a third party. Then, the third party who accepts the provision makes the nitride without adding rare-earth elements The semiconductor layer is grown on the substrate provided with the nitride layer added with rare earth elements to manufacture a nitride semiconductor device, and the same effect can also be obtained.

That is to say, the invention described in item 8 of the scope of patent application,

A substrate used in the manufacture of nitride semiconductor devices, characterized in that:

The substrate is constituted by providing a rare earth element-added nitride layer on an obliquely inclined substrate, and the aforementioned rare-earth element-added nitride layer is a rare earth element added.

Moreover, the invention described in item 9 of the scope of patent application,

The substrate described in item 8 of the scope of patent application, wherein the nitride layer added with rare earth elements is formed by adding the rare earth elements to GaN, InN, AlN, or any two or more of these mixed crystals. Floor.

Also, the invention described in item 10 of the scope of patent application,

The substrate according to item 8 or 9 of the scope of patent application, wherein the addition concentration of the rare earth element in the rare earth element added nitride layer is 0.001 to 10 at%.

Moreover, the invention described in item 11 of the scope of patent application,

The substrate according to any one of items 8 to 10 in the scope of patent application, wherein the thickness of the nitride layer to which the rare earth element is added is 0.1 nm or more.

Also, the invention described in item 12 of the scope of patent application,

The substrate according to any one of items 8 to 11 in the scope of patent application, wherein the aforementioned rare earth element is Eu.

Moreover, the invention described in item 13 of the scope of patent application,

The substrate according to any one of items 8 to 12 of the scope of patent application, wherein the aforementioned oblique angled substrate is any one of sapphire, SiC, Si, or is made of GaN, InN, AlN, or any two of these Nitride semiconductor composed of mixed crystals of more than one.

In the above-mentioned nitride semiconductor device and substrate of the present invention, the nitride layer added with a rare earth element can be achieved by using the organometallic vapor phase epitaxial growth method (OMVPE method) to change the temperature condition while not on the way. A series of steps taken out of the reaction vessel is to form a nitride layer without rare earth element and a nitride layer with rare earth element added on an obliquely inclined substrate.

Here, before forming the nitride layer containing rare earth elements, the nitride layer without adding rare earth elements is formed because, for example, sapphire and GaN, the lattice constants of the oblique inclined substrate and the nitride layer are different, and it is considered When propagating crystal defects in the obliquely inclined substrate, it is better to provide a nitride layer without rare earth element addition between the obliquely inclined substrate and the nitride layer added with rare earth elements. Specifically, the LT (Low Temperature; low temperature)-nitride layer without added rare earth elements grown at low temperature and ud (Undoped; Undoped)-nitride layers, two types of nitride layers without added rare earth elements are preferred.

By setting the LT-nitride layer, the lattice of the substrate and the nitride layer can be tilted at an oblique angle The constant is suitable and prevents cracking. Moreover, by providing the ud-nitride layer, the dislocation of crystal defects can be suppressed and high-quality nitride crystals can be obtained.

Specifically, first, in the same manner as in the past, the LT-nitride layer and the ud-nitride layer are formed on the oblique angle substrate as a nitride layer without added rare earth elements. Subsequently, the temperature was changed from 900 to 1100° C. to form a rare earth element-added nitride layer on the rare-earth element-free nitride layer.

At this time, the surface of the nitride layer to which the rare earth element is added is flattened by the surfactant effect of the added rare earth element. Therefore, even if the nitride semiconductor layer is provided on the nitride layer to which the rare earth element is added as the base treatment layer to manufacture the nitride semiconductor device, there is no giant step, and the nitride semiconductor exhibiting excellent device characteristics can be stably supplied. Device.

In addition, a nitride layer (LT-nitride layer, ud-nitride layer) without rare-earth element addition and a nitride layer with rare-earth element addition are formed, and then a nitride semiconductor layer is formed, because in each nitride layer The growth can be performed by only setting the change of temperature conditions and whether to add rare earth elements, so it can be performed in a series of steps without taking it out of the reaction vessel.

In addition, in the above, the process is performed in advance until the nitride layer to which the rare earth element is added is formed, and the nitride semiconductor device can be manufactured by using this as a substrate and forming the nitride semiconductor layer.

The inventions described in items 14 to 17 of the scope of application for patents are invented based on the above-mentioned insights, and the inventions described in item 14 of the scope of application for patents are invented,

A method for forming a rare earth element-added nitride layer is to form a rare-earth element-added nitride layer on an obliquely inclined substrate. The foregoing forming method includes the following steps:

The step of forming a nitride layer without added rare earth elements on the aforementioned obliquely inclined substrate; and

A nitride layer with rare earth elements added is formed on the aforementioned nitride layer without rare earth elements The steps;

The foregoing steps are performed by using the organometallic vapor phase epitaxial growth method without taking out a series of formation steps from the reaction vessel, and,

The aforementioned rare earth element-added nitride layer is formed at a temperature of 900 to 1100°C.

Moreover, the invention described in item 15 of the scope of patent application,

A substrate, characterized in that:

On the obliquely inclined substrate, a nitride layer containing no rare earth element and a nitride layer containing a rare earth element are formed sequentially stacked.

Also, the invention described in item 16 of the scope of patent application,

A method for manufacturing a nitride semiconductor device is to form a nitride semiconductor layer on a rare earth element-added nitride layer formed using the method for forming a rare-earth element-added nitride layer as described in the scope of patent application 14, And manufacture nitride semiconductor devices.

Also, the invention described in item 17 of the scope of patent application,

A nitride semiconductor device in which a nitride layer without rare-earth elements, a nitride layer with rare-earth elements, and a nitride semiconductor layer are sequentially laminated on an obliquely inclined substrate.

As mentioned above, the present inventors succeeded in manufacturing a red light-emitting diode by using a Eu-added GaN layer as an active layer (light-emitting layer) in the world, but there is an increasing demand for further enhancing its luminous intensity.

The present inventors are conducting research on the further improvement of the luminous intensity of this red light-emitting diode. For example, the red light-emitting diode with Eu-added GaN layer as the active layer is used in the light emission of rare earth ions. In the device, because the high-concentration doping system of rare-earth elements directly contributes to the increase in luminous intensity, it is considered that the crystal growth technology that can add rare-earth elements at a high concentration is not May be lacking and specific discussions have been conducted.

As a result, it is known that in the growth of nitride semiconductor thin films, the orientation is slightly inclined several degrees along the crystal axis from the [0001] direction, that is, the crystal growth of the Eu-added GaN layer of the active layer is performed using the obliquely inclined substrate. At this time, because a strong step flow growth mechanism can be obtained, Eu can be doped at a high concentration.

Specifically, it is known that when the Eu-added GaN layer is grown on the slightly inclined surface of the obliquely inclined substrate, it can induce a strong step flow growth mechanism and promote the step flow growth in the full range, even if it is larger than the positive axis (on-axis) Eu/Ga flow rate ratio (Eu/Ga ratio) of 2.4% Eu/Ga ratio is considered the best growth condition for the growth of Eu-added GaN layer on the substrate. Eu is also efficiently stored in The active layer and the Eu-added GaN layer system gradually grows while maintaining the quality (high crystallinity) of the GaN film and can obtain very excellent emission intensity.

That is, the growth of the Eu-added GaN layer on the normal axis substrate in the past is due to the increase in the concentration of Eu, which produces a unique hillock structure on the surface and easily becomes a rough growth surface. The low crystal quality hinders the increase of luminous intensity. Moreover, in a high current injection, that is, a high excitation state, the luminous intensity is saturated and causes a phenomenon called a drop in efficiency. Therefore, in the past, in the formation of Eu-added GaN layers, it is considered that the Eu/Ga ratio of 2.4% is the optimal growth condition. However, in the present invention, the Eu/Ga ratio is increased and Eu is added as described above. The GaN layer is grown on an obliquely inclined substrate, and since the bump structure formed with the addition of Eu is suppressed, and the Eu-added GaN layer containing Eu in a high concentration is formed, very excellent luminous intensity can be obtained.

When O is added to the luminous intensity system together with Eu, the local structure swing in the periphery of Eu of the active layer is sharply reduced, the luminescence spectrum (PL spectrum) is sharpened, and the luminous intensity is increased. Therefore, the Eu-added GaN layer system It is better to be a GaN layer in which Eu and O are added together.

Moreover, this red light-emitting device can also be manufactured using an obliquely inclined substrate that has been subjected to the above-mentioned base treatment in advance. However, since the base treatment layer is also a Eu-added GaN layer, the Eu-added GaN layer is directly formed at the oblique angle. Preferably on the substrate. That is, because the Eu-added GaN layer formed at the initial stage functions as the base treatment layer of the obliquely inclined substrate, and the Eu-added GaN layer formed thereon functions as the active layer, it can be used for base treatment Under the state of the environment, the substrate treatment and the formation of the active layer are carried out in a series of steps, and the formation of the active layer can be carried out more efficiently. In addition, since Eu can be effectively used, a high material gain can be obtained.

In addition, even when Pr (鐠) is used instead of Eu as the added rare earth element, such a significant increase in luminous intensity can be obtained in the same way. At this time, the Pr-added GaN layer may be directly formed on the oblique angle substrate. However, it is preferable to form the Pr-added GaN layer on the oblique angle substrate that has been subjected to the base treatment in advance as the active layer.

The inventions described in items 18 to 22 of the scope of patent application are inventions based on the above insights, and the inventions described in item 18 of the scope of patent applications are inventions,

A red light emitting device, characterized in that:

Eu or Pr is added as a rare earth element to GaN, InN, AlN, or any two or more of these mixed crystals, and a rare earth element-added nitride layer is formed as an active layer,

The aforementioned active layer is formed on the substrate as described in any one of items 8 to 13 in the scope of the patent application.

Moreover, the invention described in item 19 of the scope of patent application,

A red light-emitting device, characterized in that: a mixed crystal of GaN, InN, AlN, or any two or more of these is formed by adding Eu as a rare earth element to a mixed crystal formed by adding a rare earth element to nitrogen物层。 Compound layer.

Also, the invention described in item 20 of the scope of patent application,

The red light-emitting device described in item 18 or 19 of the scope of patent application, wherein the aforementioned rare earth element-added nitride layer is co-added with oxygen-added rare-earth element nitride layer.

Also, the invention described in item 21 of the scope of patent application,

A method for manufacturing a red light-emitting device is a method for manufacturing a red light-emitting device as described in item 19 of the scope of patent application, characterized in that: the organic metal vapor phase epitaxial growth method is used to add Eu and nitrogen with rare earth elements. The compound layer is formed on the obliquely inclined substrate.

According to the present invention, when a nitride semiconductor layer is formed on an obliquely inclined substrate to manufacture a semiconductor device, there is no risk of lattice deformation and crystal defects caused by the mixed crystal of In and GaN, and there is no need to continue adding The material prevents the generation of giant steps, so it can provide a manufacturing technology for the nitride semiconductor layer that can stably supply high-quality semiconductor devices.

10‧‧‧Sapphire substrate

20‧‧‧LT-GaN layer

30‧‧‧ud-GaN layer

40‧‧‧Eu-added GaN layer

50‧‧‧Cover

c‧‧‧c distance between faces

θ‧‧‧bevel angle

Fig. 1 is a schematic diagram showing the structure of a nitride semiconductor device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the outline of the formation of a nitride semiconductor device in an embodiment of the present invention.

Fig. 3 is a diagram showing the result of observing the reflection intensity of the opposite surface from the laser irradiated on the growing GaN layer on the spot in an embodiment of the present invention. (a) is the substrate tilted at an oblique angle, (b ) Is the observation result on the positive axis substrate.

Figure 4 is a diagram showing the results of observing the surface of each GaN layer without Eu addition after growth using an optical microscope (upper section) and AFM microscope (lower section) in an embodiment of the present invention. (a) is on the positive axis base Plate, (b) is the observation result of tilting the substrate at an oblique angle.

Figure 5 is a graph showing the result of observing the reflection intensity of the laser irradiated on the growing GaN layer on the spot in one embodiment of the present invention. (a) is the substrate tilted at an oblique angle, and (b) is the positive Observation results of the shaft substrate.

Fig. 6 is a diagram showing the result of observing the surface of the cover layer using an AFM microscope in one embodiment of the present invention, (a) is the observation result on the normal axis substrate, and (b) is the observation result on the oblique angle of the substrate.

Fig. 7 is a diagram showing the result of observing the surface of the sample with the Eu-added GaN layer provided on the obliquely inclined substrate using (a) an optical microscope and (b) an AFM microscope in one embodiment of the present invention.

Fig. 8 is a diagram illustrating crystal growth using obliquely inclined substrates.

Figure 9 is a diagram showing the relationship between the bevel angle and the platform width.

Fig. 10 is a schematic diagram showing the structure of a red light emitting device formed with a GaN layer added with Eu.

Figure 11 is an optical microscope image of the surface of a GaN layer co-added with Eu and O formed using a normal axis substrate.

Fig. 12 is a diagram illustrating the difference in the surface state of the Eu and O co-added GaN layer formed by using an oblique angle substrate and a normal axis substrate.

Figure 13 is a graph showing the results of measuring the PL spectrum of a red light-emitting device with Eu-added GaN layers formed on a normal axis substrate and a diagonally inclined substrate at room temperature. (a) shows the PL spectrum intensity (au) The relationship with wavelength (nm), (He-Cd laser, 5mW excitation), (b) shows the relationship between the excitation power (mW) and the PL integrated intensity (au) at the wavelength of 610 to 650 nm.

Specific embodiments are listed below, and the present invention will be explained using figures. And again In the following description, a sapphire substrate is used as an oblique angle substrate, GaN is used as a nitride, and Eu is used as a rare earth element as examples, but as described above, it is not limited to these examples.

1. Nitride semiconductor device

Fig. 1 is a schematic diagram showing the structure of a nitride semiconductor device according to an embodiment of the present invention. In Fig. 1, a 10-series sapphire substrate, a 40-series Eu-added GaN layer (GaN:Eu), and a cap layer 50 are formed on the Eu-added GaN layer 40. In addition, the cap layer 50 is a GaN layer (ud-GaN) with no Eu added as a nitride semiconductor layer.

In this embodiment, as the base treatment layer when the cover layer 50 is formed, the Eu-added GaN layer 40 with Eu and exhibits an excellent surfactant effect is provided. Therefore, even if the cover layer 50 can be grown On the Eu-added GaN layer 40 to prevent the generation of giant steps, even if the thickness is greater than 5 μm, it can be grown at the atomic level while forming a flat surface. Furthermore, by using the originally expected obliquely inclined substrate to fully exhibit the effect of crystal growth, the device characteristics can be improved.

In this way, in this embodiment, the effect of flattening the surface of the Eu-added nitride layer provided as the base treatment layer can be maintained even if it is formed in the upper cover layer (nitride semiconductor layer). Stable supply of suitable nitride semiconductor devices, not only as light-emitting devices, but also as high-frequency devices and high-output devices.

Also, in this embodiment, as shown in FIG. 1, between the sapphire substrate 10 and the Eu-added GaN layer 40, there is provided an LT-GaN layer 20 grown at a low temperature of about 475°C, and a Two types of Eu-free GaN layers (ud-GaN) 30 grown at a high temperature of about 1180°C. As mentioned above, by providing the LT-GaN layer 20, the lattice constants in the sapphire crystal and GaN crystal can be adapted and the generation of cracks can be prevented. Moreover, by providing the ud-GaN layer 30, It can suppress the influence of the difference of crystal defects and control the generation of defects in the Eu-added GaN layer.

2. Method of forming nitride semiconductor device

Next, a method of forming the aforementioned nitride semiconductor device will be described. FIG. 2 is a diagram showing the outline of the formation of the nitride semiconductor device in this embodiment. Also, in the second graph, the gas supplied as a raw material and the supply rate are displayed in the upper row, and the relationship between the growth temperature (vertical axis) and time (horizontal axis) is displayed in the lower column.

In this embodiment, the OMVPE method is used when forming the nitride semiconductor device. Furthermore, trimethylgallium (TMGa) is used as the Ga raw material and ammonia (NH ₃ ) is used as the N raw material. In addition, as a raw material for Eu, n-propyltetramethylcyclopentadienyl europium (Eu[C ₅ (CH ₃ ) ₄ (C ₃ H ₇ ), which is formed by bubbling carrier gas (hydrogen: H ₂ ) )] ₂ : EuCp ^pm ₂ ).

Furthermore, as shown in FIG. 1, the LT-GaN layer 20, the ud-GaN layer 30, the Eu-added GaN layer 40, and the capping layer 50 are sequentially formed on the sapphire substrate 10 according to the outline shown in FIG. The following is a specific description based on the first and second figures.

(1) Formation of LT-GaN layer 20

First, the sapphire substrate 10 inclined at an oblique angle of 1° was placed in a reaction vessel adjusted to a pressure of 104 kPa. Then, the temperature in the reaction vessel was set to 475° C., and NH ₃ gas (223 mmol/min) and TMGa Gas (52.1 μmol/min) was supplied into the reaction vessel, and the LT-GaN layer 20 with a thickness of 30 nm was formed on the sapphire substrate 10 at a growth rate of 1.3 μm/h.

(2) Formation of ud-GaN layer 30

Next, the temperature in the reaction vessel 1180 is set deg.] C, the NH ₃ gas (179mmol / min) and TMGa gas (102μmol / min) fed into the reaction vessel, and the growth rate to a thickness of 2μm to 3.2μm h ud- / The GaN layer 30 is formed on the sapphire substrate 10.

(3) Formation of Eu-added GaN layer 40

Next, set the temperature in the reaction vessel to 960°C, supply NH ₃ gas (179 mmol/min), TMGa gas (25.6 μmol/min), and EuCp ^pm ₂ gas (0.586 μmol/min) into the reaction vessel, and The Eu-added GaN layer 40 with a thickness of 40 nm is formed on the ud-GaN layer 30 at a growth rate of 0.78 μm/h.

(4) Formation of cover layer 50

Next, set the temperature in the reaction vessel to 1180°C again, supply NH ₃ gas (179mmol/min) and TMGa gas (102μmol/min) into the reaction vessel, and cover the thickness of 5μm at a growth rate of 3.2μm/h The layer 50 is formed on the Eu-added GaN layer 40 and serves as a nitride semiconductor device.

Also, in the above, EuCp ^pm _{2 with} high vapor pressure is used as the raw material of Eu, but Eu(C ₁₁ H ₁₉ O ₂ ) ₃ , Eu[C ₅ (CH ₃ ) ₅ ] ₂ , Eu[C ₅ ( CH ₃ ) ₄ H] ₂ and so on.

3. Evaluation

(1) Confirmation of the generation of giant steps in the obliquely inclined substrate

As an evaluation sample, a 7.6 μm thick GaN layer without added Eu was grown on a sapphire substrate (oblique oblique substrate) inclined at an oblique angle of 1° using the OMVPE method. On the other hand, for comparison, the same procedure was carried out and a 7.6 μm thick GaN layer without added Eu was grown on a non-tilted sapphire substrate (normal axis substrate).

Then, each growing GaN layer was irradiated with a laser with a wavelength of 633 nm, and the intensity of reflection from the surface was observed on the spot. The results are shown in Figure 3. Also, in Figure 3, (a) is the oblique angle of the substrate, (b) is the observation result of the positive axis substrate, the vertical axis on the left of each is the reflection intensity (arb.unit), and the vertical axis on the right is the crystal Growth temperature (°C), and the horizontal axis represents crystal growth time (min).

In the case of a normal-axis substrate, as shown in Figure 3(b), the overall reflection intensity is relatively high, and the crystal growth time is maintained at a certain level. In contrast, when the substrate is tilted at an oblique angle, as shown in Figure 3(a), it can be seen that the overall reflection intensity becomes lower, and it changes according to the crystal growth time. Long and the reflection intensity is further reduced. It is believed that this is because the nitride layer is formed on the oblique angle substrate, so the flatness in the surface of the nitride layer is low and the flatness further decreases as the film thickness becomes thicker.

At the same time, an optical microscope and an AFM microscope (atomic force microscope) were used to observe the surface of each Eu-added GaN layer after growth and evaluate its surface state. The results are shown in Figure 4. Also, in Figure 4, the upper section shows the observation results using an optical microscope, and the lower section shows the observation results using an AFM microscope. The left side is (a) the normal axis substrate, and the right side is the (b) oblique angle tilted substrate. .

As shown in Figure 4, in the case of a positive axis substrate, the giant steps cannot be observed and the surface is flat. On the other hand, when the substrate is inclined at an oblique angle, huge giant steps caused by step folds can be observed, a wavy structure is generated on the surface, and flatness is impaired.

(2) Evaluation of flatness of GaN layer without Eu addition

Next, as evaluation samples, a 30nm thick LT-GaN layer, a 2μm thick ud-GaN layer, a 40nm thick Eu-added GaN layer, and a 5μm thick cover layer (ud-GaN layer) were grown on the same On the substrate (oblique angle substrate and normal axis substrate). On the other hand, for comparison, the ud-GaN layer is grown on each substrate until the total thickness becomes the same thickness.

In the same manner as above, the reflection intensity of each layer during growth was observed on the spot, and the surface of each GaN layer in the uppermost layer after growth was observed using an AFM microscope and an optical microscope, and the surface state was evaluated.

The observation result of the reflection intensity is shown in Figure 5. Also, in Figure 5, the upper section (a) is the observation result of the substrate tilted at an oblique angle, the lower section (b) is the observation result of the substrate on the normal axis, the left side is the observation result of all steps, and the right side is the observation result of the cover layer. Observations in growth. In addition, the solid line is the observation result of the sample with the Eu-added GaN layer, and the broken line is the sample with the ud-GaN layer only.

In the case of a normal axis substrate, as shown in Figure 5(b), the GaN with Eu The reflection intensity in the sample of the layer has little change from the reflection intensity in the sample with only the ud-GaN layer, and it can maintain a certain level even if the crystal growth time becomes longer. In contrast, when the substrate is tilted at an oblique angle, as shown in Figure 5(a), by providing a Eu-added GaN layer, the reflection intensity can be drastically improved compared to the sample with only the ud-GaN layer. From this result, it is understood that the growth of the Eu-added GaN layer has a significant impact on the improvement of flatness when the cap layer is formed.

Figure 6 shows the result of observing the surface of the cover layer using an AFM microscope. Also, here, the observation results on the sample provided with the Eu-added GaN layer are shown, (a) on the normal axis substrate, and (b) on the oblique angle of the substrate.

It can be seen from Fig. 6 that the Eu-added GaN layer is placed on the obliquely inclined substrate to achieve the same surface state as the normal axis substrate.

Fig. 7 shows the results of using (a) an optical microscope and (b) an AFM microscope to observe the surface of a sample in which the Eu-added GaN layer is placed on an obliquely inclined substrate.

From Fig. 7, it is known that by providing the Eu-added GaN layer, the surface of the capping layer is smoothed and its surface roughness RMS becomes very small 0.15nm. The result is that the generation of giant steps is prevented by the addition of Eu, and it is shown that a GaN layer with a flat surface is formed at an atomic level and that Eu has an excellent surfactant effect.

In addition, in the above, an example in which a Eu-added GaN layer is grown on an obliquely inclined substrate and a cover layer is provided on it is given, and the effect of the surfactant is explained, but the Eu-added GaN layer can also be used The ud-GaN layer and the ud-GaN layer are stacked multiple times in pairs, whereby the surface state can be further smoothed.

4. Application in semiconductor devices

As mentioned above, in this embodiment, the Eu-added GaN layer is placed on the obliquely inclined substrate Above, a low defect density substrate can be provided. Therefore, compared to the past, blue/green LEDs with high luminous efficiency can be achieved drastically. In addition, since low row density is achieved on the obliquely inclined substrate, a device with less leakage can be realized and a highly reliable nitride power device can be manufactured.

5. Red light-emitting device

Next, the red light emitting device of this embodiment will be described in detail.

(1) Problems with prior art

Initially, the problems in the growth of the Eu-added GaN layer on the conventional normal axis substrate are explained. Specifically, it is explained why the Eu/Ga ratio is set to be 2.4% for the optimal growth condition of the Eu-added GaN layer.

First, as a sample for evaluation, a red light-emitting device was manufactured by changing the Eu/Ga ratio at 2.4%, 3.5%, and 7.1% and forming a GaN layer co-added with Eu and O on a normal axis substrate.

Specifically, an additive-free GaN layer (LT-GaN layer and ud-GaN layer) with a thickness of about several μm is first grown on a normal-axis sapphire substrate, and then TMGa is used as the Ga raw material and NH _{3 is} used as the N raw material. EuCp ^pm ₂ bubbled with a carrier gas (supplied with oxygen) is used as a raw material of Eu, introduced at a predetermined Eu/Ga ratio and grown into a GaN layer with a thickness of about 300 nm with Eu and O added. Finally, it was grown into a ud-GaN layer with a thickness of 10 nm and three types of red light-emitting devices were manufactured (refer to Fig. 10).

Figure 11 is an optical microscope image of the surface of the GaN layer with Eu and O added in the three types of evaluation samples obtained. Figure 11 shows that in the case of a positive axis sapphire substrate, as the Eu/Ga ratio increases to 2.4%, 3.5%, and 7.1%, the surface flatness gradually disappears, especially from 3.5% to 7.1% At this time, the crystal growth surface is significantly degraded.

Moreover, in the upper part of Figure 12, the surface state of the GaN layer with Eu and O added in the two cases of Eu/Ga ratio of 3.5% and 7.1% is compared with the optical microscope in Figure 11. Magnification display. From Figure 12, it is known that when a GaN layer co-added with Eu and O is formed on a normal axis substrate, because the active layer grows spirally, as the Eu/Ga ratio increases, many spiral protrusions are formed and the surface is formed Rough.

In addition, Fig. 13 shows the result of measuring the PL spectrum of the Eu-added GaN layer formed on the normal axis substrate at room temperature. In addition, in Figure 13, (a) shows the relationship between PL spectral intensity (au) and wavelength (nm) (He-Cd laser, 5mW excitation), (b) shows the excitation power (mW) and the The relationship between the PL integrated intensity (au) in the wavelength 610 to 650nm.

From Figure 13(a), it is known that in the case of a positive axis substrate, as the Eu/Ga ratio increases, the emission peak of ⁵ D ₀ → ⁷ F ₂ at the emission center increases. However, on the other hand, as shown in Figure 13(b), even if the Eu/Ga ratio is increased under strong excitation, the saturation of the luminescence is enhanced, and when the Eu/Ga ratio is 7.1%, the luminous intensity is slightly reduced compared to 3.5%. .

Therefore, in consideration of the surface state of the Eu-added GaN layer, the optimal growth conditions for growing the Eu-added GaN layer on the normal axis substrate is the Eu/Ga ratio of 2.4%, and the Eu/Ga ratio is increased by more than this. Than it was considered a problem.

(2) Eu-added GaN layer formed on obliquely inclined substrate

Next, as the present embodiment, the surface state and luminous intensity when the Eu-added GaN layer is formed on the obliquely inclined substrate will be described.

The inventors of the present invention, as mentioned above, focused on obtaining a strong step flow growth mechanism when crystal growth was performed along the orientation slightly inclined several degrees from the crystal axis of the [0001] direction during the growth of nitride semiconductor thin films. The Eu-added GaN layer is formed on the obliquely inclined substrate.

Specifically, on a slightly inclined (0001) sapphire substrate with an oblique angle of 2° in the m-axis direction, two types of Eu/Ga ratios of 3.5% and 7.1% were produced in the same manner as the above-mentioned normal axis substrate. Red light emitting device.

In the lower part of Figure 12, the surface state of the obtained GaN layer with Eu and O added is shown. From Figure 12, it is known that in the case of obliquely inclined substrates, because the growth of the active layer is not spiral growth, but step flow growth, the formation of spiral protrusions is suppressed, and even if the Eu/Ga ratio changes High, it also makes the active layer grow while maintaining high crystallinity.

In addition, in Fig. 13, the PL spectrum measurement result of the Eu/Ga ratio 3.5% formed on the obliquely inclined substrate is also shown. From Fig. 13(a), it is known that when the substrate is inclined at an oblique angle, even if the Eu/Ga ratio is set to 3.5%, a strong luminous intensity that cannot be obtained in a normal-axis substrate is obtained. Also, from Figure 13(b), it can be seen that the saturation of light emission is suppressed, and the light emission intensity is increased by 2.04 times compared to the conventional positive axis substrate (Eu/Ga ratio 2.4%).

This increase in luminous intensity is due to the same Eu/Ga ratio, because the Eu introduced into the active layer increases the Eu concentration in the Eu-added GaN layer, so the Eu-added GaN layer is formed at an oblique angle On the inclined substrate, a high Eu concentration Eu-added GaN layer can be formed, and it can be confirmed that it is promising as a method for improving the luminous intensity.

(3) The usefulness of the red light-emitting device of this embodiment

As described above, in the red light-emitting device of this embodiment, since the Eu-added GaN layer with a high Eu concentration can be formed on the obliquely inclined substrate, it can directly contribute to the development of strong luminous intensity, so it can be manufactured with high efficiency The red light-emitting device of GaN is applied to the semiconductor LED in the visible light region developed with GaN-based materials as the center, and can realize high-brightness light-emitting diodes. In addition, in the development of a laser diode containing a rare-earth-added semiconductor layer that has attracted attention in recent years as an active layer, a high-concentration addition of rare-earth elements such as Eu can obtain higher materials. Gain.

Above, the present invention has been described based on the embodiments, but the present invention is not implemented by the above Shape limitation. Various changes can be added to the above-mentioned embodiment within the same and equal range as the present invention.

10‧‧‧Sapphire substrate

20‧‧‧LT-GaN layer

30‧‧‧ud-GaN layer

40‧‧‧Eu-added GaN layer

50‧‧‧Cover

Claims (19)

A nitride semiconductor device is formed by providing a nitride semiconductor layer on a substrate, wherein the substrate is an obliquely inclined substrate, a nitride layer without rare earth elements is provided on the substrate, and no rare earth is added to the substrate. The nitride layer of elemental elements is provided with a nitride layer of rare earth elements as a base treatment layer. The nitride layer of rare earth element is added with Eu or/and Pr as rare earth elements. A nitride semiconductor layer is provided on the elemental nitride layer. The nitride semiconductor device described in claim 1, wherein the nitride layer with the rare earth element added is a mixed crystal in which the rare earth element is added to GaN, InN, AlN, or any two or more of these Into the layer. The nitride semiconductor device described in item 1 or 2 of the scope of the patent application, wherein the addition concentration of the rare earth element in the nitride layer to which the rare earth element is added is 0.001 to 10 at%. In the nitride semiconductor device described in item 1 or 2 of the scope of patent application, the thickness of the nitride layer to which the rare earth element is added is 0.1 nm or more. The nitride semiconductor device described in item 1 or 2 of the scope of patent application, wherein the rare earth element is Eu. The nitride semiconductor device described in item 1 or 2, wherein the aforementioned substrate is any one of sapphire, SiC, Si, or is made of GaN, InN, AlN, or a mixture of any two or more of these Nitride semiconductor composed of crystal. The nitride semiconductor device described in item 1 or 2 of the scope of patent application is any one of a light emitting device, a high frequency device, and a high output power device. A substrate for manufacturing a nitride semiconductor device is used when manufacturing a nitride semiconductor device. The substrate for manufacturing a nitride semiconductor device includes a nitride layer without rare earth elements added on an obliquely inclined substrate and A nitride layer added with a rare earth element is provided on the nitride layer without the addition of a rare earth element, and the nitride layer with a rare earth element added is one in which Eu or/and Pr are added as a rare earth element. The substrate for manufacturing a nitride semiconductor device according to the eighth patent application, wherein the nitride layer with the rare earth element added is the rare earth element added to GaN, InN, AlN, or any two or more of these The layer of mixed crystals. The substrate for manufacturing a nitride semiconductor device according to item 8 or 9 of the scope of patent application, wherein the rare earth element is added at a concentration of 0.001 to 10 at% in the rare earth element-added nitride layer. The substrate for manufacturing a nitride semiconductor device as described in item 8 or 9 of the scope of patent application, wherein the thickness of the nitride layer to which the rare earth element is added is 0.1 nm or more. The substrate for manufacturing a nitride semiconductor device according to item 8 or 9 of the scope of patent application, wherein the rare earth element is Eu. The substrate for manufacturing a nitride semiconductor device as described in item 8 or 9 of the scope of patent application, wherein the aforementioned oblique angled substrate is any one of sapphire, SiC, Si, or is made of GaN, InN, AlN, or the like Nitride semiconductor composed of mixed crystals of any two or more. A method for forming a rare earth element-added nitride layer is formed by forming a rare-earth element-added nitride layer on an obliquely inclined substrate. The aforementioned forming method includes the following steps: forming a rare-earth element-free nitride layer Steps on the aforementioned obliquely inclined substrate; and The step of forming a rare earth element-added nitride layer on the aforementioned non-additional rare-earth element nitride layer, wherein the aforementioned rare-earth element-added nitride layer is one with Eu or/and Pr added; by using organic metal The vapor phase epitaxial growth method does not take out a series of forming steps from the reaction vessel and performs the foregoing steps, and forms the foregoing rare earth element-added nitride layer at a temperature of 900 to 1100°C. A substrate for manufacturing a nitride semiconductor device is formed on an obliquely inclined substrate with a nitride layer without rare earth elements and a nitride layer with rare earth elements added in sequence, wherein the aforementioned rare earth elements are added The elemental nitride layer is one added with Eu or/and Pr. A method for manufacturing a nitride semiconductor device is to form a nitride semiconductor layer on a rare earth element-added nitride layer formed using the method for forming a rare-earth element-added nitride layer as described in the 14th patent application , And manufacturing nitride semiconductor devices. A nitride semiconductor device in which a nitride layer without rare-earth elements, a nitride layer with rare-earth elements, and a nitride semiconductor layer are sequentially laminated on an obliquely inclined substrate, wherein the aforementioned rare-earth is added The nitride layer of the similar element is one with Eu or/and Pr added. A red light-emitting device in which Eu or Pr is added as a rare earth element to a mixed crystal of GaN, InN, AlN, or any two or more of these, and a nitride layer system with a rare earth element added is formed as an active layer, The aforementioned active layer is formed on the substrate for manufacturing a nitride semiconductor device as described in any one of items 8 to 13 in the scope of the patent application. The red light-emitting device described in item 18 of the scope of patent application, wherein the aforementioned rare-earth element-added nitride layer is co-added with oxygen-added rare-earth element nitride layer.

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